Toll-like receptors are critical sensors of microbial infection, responsible for the induction of the inflammatory, innate and adaptive immune responses. Over the past few years, significant progress has been made in elucidating the TLR signaling pathways. It has been defined that four signaling adapters: MyD88, TIRAP, TRIP and TRAM, are used by TLRs to induce distinct signaling pathways. While the role of these adapters has been clearly defined genetically, the biochemical and cell biological mechanisms of their functions are almost completely unknown. In this proposal, we plan to investigate the cell biology of TLR signaling, with the emphasis on the signaling adapters. Based on preliminary studies, our plan is to analyze the processes that control sub-cellular distribution of these adapter proteins, their mechanisms of recruitment to the receptors, and the engagement of the downstream signaling components. As the critical sensors of microbial infection capable of inducing powerful inflammatory responses, TLRs must combine the exquisite sensitivity to their ligands, with robust regulation to ensure the fidelity of the responses they induce. Elucidation of the cell biological principles of TLR signal transduction will help to understand the fundamental biology of the innate immune recognition.